ARDL's methodology flowchart for the shelf life of products and the service life of engineered parts is shown below. The first step is to define the function(s) of the component. Based on the function, a failure criterion is established. The failure criterion may be defined as an unacceptable change in the function which causes a particular failure. Changes may be in stress relaxation, stiffness/modulus, creep, tear resistance, swelling, dielectric properties, etc. The underlying mechanism involved in this change is identified and characterized. The rate of change is then determined by an accelerated laboratory test at different levels of severity and at different time intervals. It is important to keep the accelerated test condition similar to the service condition and perform the test at multiple temperatures higher than the average service temperature.